Apparatus for directional tubing perforation



Sept. 19, 1967 N. J. MELLIES 3,342,275

APPARATUS FOR DIRECTIONAL TUBING PEHFORATION Filed Sept, 5, 1963 r 4 Sheets-Sheet 1 SURFACE POWER AND CONTROL EQUIPMENT INVENTOR.

NORMAN J. MELLIES Y ATTORNEY p 1957 N. J. MELLIES APPARATUS FOR DIRECTIONAL TUBING PERFORATION 4 Sheets-Sheet 2 Filed Sept. 5, 1963 INVENTOR.

NORMAN J. MELLIES ATTORNEY Sept. 19, 1967 N. J. MELLIES APPARATUS FOR DIRECTIONAL TUBING PERFORATION Filed Sept. 5, 1963 4 Sheets-Sheet 3 To surface control and I5A recording equipment FIG. 3

IIB

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INVENTOR.

NORMAN J. MELLIES ATTORNEY United States Patent 3,342,275 APPARATUS FOR DIRECTIONAL TUBING PERFORATION Norman J. Mellies, Houston, Tex., assignor to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed Sept. 5, 1963, Ser. No. 306,843 5 Claims. (CI. 1.75-4.51)

This invention is related to the recovery of petroleum from subsurface earth formations, and more particularly relates to methods and apparatus for use in selectively completing oil and gas wells having a plurality of production zones. Specifically, this invention relates to improved methods and apparatus for selectively perforating one of a plurality of tubing strings arranged in a common borehole in side-by-side relationship.

Many techniques have been developed for achieving completion of an oil or gas well in a manner such that a plurality of formations are tapped without commingling of production. Generally, all such techniques require the installation of easing throughout the entire length of the borehole. A packer is then inserted in the casing at a point above the deepest formation of interest, and one or more packers are thereafter inserted at succeeding levels above the next formations proceeding upwards. In the case of a dually completed well (tapping only two formations) only the one packer is required, and if it is intended that one formation be produced through the casing, a single string of tubing is inserted in the casing and through the packer to a point opposite the deep formation. Then if the casing is perforated at a point adjacent the higher formation of interest, the shallow formation may be produced through the casing surrounding the tubing, and the deep formation may be produced through the tubing. The packer, of course, serves the purpose of separating the two streams of production in the cased borehole.

Different conditions, of course, call for different tech niques. For example, it is usually not practical to pump a formation that has been completed through casing. In addition, it is often desirable to tap and produce three or more formations through a common borehole. Thus, two or more strings of tubing may be required in the casing. Sometimes it is convenient to arrange these multiple tubing strings concentrically in the casing (one inside another), but more often the strings are arranged side by side. In all cases, however, it has heretofore been the practice to install the aforementioned casing. Recently a new technique has been developed and successfully used which involves inserting the required tubing strings (one per formation) into an uncased borehole, side by side, and thereafter filling the borehole with cement to support the tubing. The tubing strings are then individually and separately perforated each at a different depth opposite a particular formation of interest, and the expense of the casin g is eliminated.

In order to appreciate the problem of selectively perforating one of a plurality of proximately associated tubing strings, it must be understood that perforation involves piercing the wall of the tubing with one or more holes. Since the perforation must obviously be accomplished from a point within the tubing, there have been made available several types of tools for performing this work. Some employ a series of laterally expanding points which are forced against the interior of the tubing (or casing) wall by the operation of jars (free-falling weights), and others employ a series of laterally driven bullets shot through the tubing wall by explosive charges. Another type of perforator employs a series of shaped charges to achieve penetration of the tubing. Some perforators have their charges or other puncturing means arranged .omni-directionally about their supporting stems. Others have their charges aligned up and down the stem so that ice perforation is achieved at various levels but in a single lateral direction. In the case of some perforators, the projectiles, charges, etc., may be singly and selectively fired whereas other types of perforators are designed for volley firing.

It is obvious that to perforate selectively one of a cluster of tubing strings a mono-directional perforator must be chosen, and that it must be positioned so that its charges are directed to avoid the other proximately positioned strings. Moreover, it is obviou that, since a laterally directed explosion will penetrate only a limited distance past the punctured tubing, it is desirable to aim the perforator towards the nearest part of the borehole wall to insure that the formation is successfully tapped. Heretofore this has been accomplished by attaching a source of radiation to the perforator suspended in the tubing string selected for perforation. This source was enclosed in shielding having an aperture or slot in one side for the purpose of restricting the radiation emitted by the source to a laterally directed narrow beam which was aimed coincidently with the discharge direction of the perforator. In order to aim the perforator it was also necessary to suspend a radiation detector in each adjacent tubing string and then to rotate the perforator until the adjacently disposed detectors sensed the least radiation, i.e., direct the beam away from the detectors and therefore away from the adjacent tubing strings. Since this direction-finding equipment cannot of itself provide a depth indication, the perforator used for such purposes was usually supplemented with a casing collar locator in addition to its other circuitry.

The chief disadvantage with this method of direction perforation is the necessity for disposing the detectors in the adjacent tubing strings. Not only is an additional hoist truck and cable required for each adjacent tubing string to be avoided, but there is the difficulty and inconvenience of suspending a detector in a tubing string which has previously been well.

Recently, novel perforating equipment and techniques have been introduced, which equipment and techniques comprise the use of a monodirectional perforator, a tubing locating means, and a rotating mechanism. These com ponents are arranged in a unitary structure whereby the perforator can be inserted into the tubing string sought to be perforated, and then rotated in a manner to direct it-away from any adjacent tubing string. The tubing 10- cator means is comprised of a monodirectional source of radiation, preferably gamma radiation, and a monodirec tional radiation detector arranged in axial spaced relationship to the source, whereby the adjacent formations and tubing strings can be scanned by rotating the apparatus in the borehole. Suitable equipment is also included at the surface for processing and recording the output signals from the detector. In operatir' the tubing locator, measurements are taken of the radiation detected by the detector, and note is made of anomalies observed in the scattering effect produced by adjacent substances upon the beam of radiation emitted by the monodirectional source. The measurements are made continuously, but are recorded linearly on a belt-like chart of conventional design, so that anomalies in the measurement may be observed which are attributable to the proximity of adjacent tubing strings, and to the nearest portion of the borehole wall.

The anomalies attributable to adjacent tubing strings, or to the nearest portion of the borehole wall, are pre sumed to be due to either the difference in the respective densities of steel and cement, or to the relative atomic numbers of the elements making up these two substances. It has also been theorized that the anomalies are sometimes due to a combination of both factors, since the experforated and completed as a flowing tent of a particular anomaly would be affected by the nature of the substances contained in an adjacent tubing string. Regardless of the actual scientific reason for these anomalies, however, they enable the new techniques and apparatus to provide a reliable indication of the relative positions of the various tubing strings in the borehole.

As hereinbefore stated, the typical apparatus currently used for such operations, includes a rotating mechanism for rotating the attached rnonodirectional perforator and pipe locator angularly about the axis of the tubing string sought to be perforated. Due to the necessity for limiting the number of electrical circuits interconnected between the surface of the earth and the detector mechanism, it has hitherto been deemed impractical to use an electri cally driven rotator. Hence, it was necessary to use a mechanical type rotator operable by raising and lowering the combined perforating apparatus longitudinally in the tubing string in a manner to rotate the perforator and pipe locator. Apparatus of this character is depicted and described in the US. Patent No. 2,998,868 which issued to M. E. True on Aug. 29, 1961.

However, such apparatus involves a number of difficulties and disadvantages which have rendered the apparatus unsuitable for use in many types of boreholes. For example, the mechanical rotator depicted in True has been found to be unreliable, because of the fact that rotation sometimes failed to occur when the tool was raised and lowered. Furthermore, there appears to be no way to indicate to the operator at the surface the fact that no rotation has in fact occurred. Also, use of this type of mechanical rotator often results in varying the depths at which the perforator is positioned in the tubing string, without any indication of such change of depth being provided at the surface. Moreover, the mechanical type rotator produces undesirable cable twist which severely limited the number of tool revolutions which might be achieved.

Another disadvantage with the equipment presently in use is the fact that the most desirable type of indication, of the character of the substances surrounding the tubing string sought to be perforated, would be a polartype of recording. However, since there was no way to synchronize the operation of the recording mechanism located at the surface, with the action of the mechanical rotator, it has hitherto been necessary to first obtain the linear type of recording hereinbefore described, and then to manually produce a polar-type of 'plot of the linear record, and this has often permitted introduction of errors which are not readily apparent.

Accordingly, it is an object of the present invention to provide novel methods and apparatus for selectively perforating one of a multiplicity of tubing strings arranged in a common borehole in side by side relationship.

It is also an object of the present invention to provide novel methods and apparatus for rotatably investigating the substances surrounding a tubing string, and deriving a synchronized and correlated polar-type of recording of the character of such substances.

Another object of the present invention is to provide novel methods and apparatus for electrically rotating a tubing perforator in a borehole, and in conjunction therewith to obtain an indication at the surface of the earth of the rotation of such perforator.

A further objective of the present invention is to provide novel methods and apparatus for employing a grounded armored cable having a single conductor to interconnect electrical signals between subsurface apparatus and the surface of the earth, such signals including firing signals for actuating a tubing perforator, power signals for actuating a radiation detector, power signals for actuating an electrically-driven rotator mechanism, signals indicative of tubing collars, and an electrical indication of the rotation of the tubing perforator.

These and other objects of the present invention will be apparent from the following detailed description d wherein reference is made to the figures in the accompanying drawings.

In the drawings:

FIGURE 1 is a cross sectional view of a borehole containing a plurality of tubing strings, and showing a tubing perforator suspended in one of said strings.

FIGURE 2 is an overhead view of the borehole and tubing strings depicted in FIGURE 1.

FIGURE 3 is a detailed view of the tubing perforator and associated equipment suspended in the tubing string depicted in FIGURE 1.

FIGURE 4 is a detailed view of a form of the apparatus used to develop an indication of the rotation of the tubing perforator depicted in FIGURES l and 3.

FIGURE 5 is a digrammatic representation of the manner in which electrical signals are transmitted between the surface and subsurface equipment employed in the present invention.

FIGURE 6 is a pictorial view of a polar recording developed by means of the present invention.

Referring now to FIGURE 1, there may be seen a cross sectional view of an uncased borehole 2 containing at least two tubing strings 5 and 6, which are composed of tubing joints 3 connected by threaded collars 4. The tubing strings 5 and 6 are supported in side-by-side relationship in cement 8. As depicted, a subsurface perforation tool assembly 9 is suspended by a cable 15 in tubing string 6 in a manner to perforate tubing string 6 without striking the adjacent tubing string 5. As will hereinafter be described in greater detail, the subsurface tool assembly 9 is composed of a suitable cable head 12, casing collar locator 13, electronics section 13B, rotator section 14, tubing locator 11, and tubing perforator 10. As depicted, the upper portion of the tool assembly 9 which includes the rotator section 14, electronics section 13B, casing collar locator 13, and cable head 12, is held in the tubing string 6 by bowspring assemblies 13A and 14A so as not to rotate. However, the tubing locator 11 and tubing perforator 10 are attached to the rotator section 14 so as to rotate about the longitudinal axis of the tubing string 6.

As hereinbefore stated, it is the object of the present invention to provide improved methods and apparatus to selectively perforate one of a plurality of tubing strings, Without striking any other tubing string. Accordingly, it is essential that the tubing perforator 10 be monodirectional in character, and that its direction of fire be correlated with the operation of the tubing locator 11 which sees the adjacent tubing strings. Any type of perforation device may be employed for these purposes, although FIGURES 1 and 3 depict a device employing the well known shaped charges for penetrating the tubing string.

Referring now to FIGURE 2, there may be seen an overhead cross sectional view of the borehole 2, and the three tubing strings 5, 6 and 7 arranged therein in sideby-side relationship. Also shown is the subsurface tool assembly 9 arranged in tubing string 6. Accordingly, it may be seen that the tubing perforator 10 may be rotated to fire in any direction generally except for the directions indicated by arrows A and B, and should preferably be aimed to fire according to arrow C since this is in the direction of the nearest portion of the Wall of the borehole 2.

Referring now to FIGURE 3, there may be seen a more detailed view of the sursurface perforating tool assembly 9 which includes a monodirectional tubing perforator 10 fixedly attached to the tubing locator 11, the cable head 12, the casing collar locator 13 and electronics section 13B, and the rotator section 14. As will hereinafter be apparent, the tubing locator 11 is pivotally attached in some suitable manner to the rotator section 14, so that the tubing locator 11 and tubing perforator 10 may be rotated within the tubing string sought to be perforated, while the upper sections of the tool 9 are fixedly supported in the tubing string 6 by means of howsprings 13A and 14A or some other suitable apparatus of conventional design.

As shown, the subsurface tool assembly 9 is adapted to be suspended, in the tubing string 6 to be perforated, by means of a cable 15 attached to the cable head 12. The cable 15 is passed over a measuring wheel 15A so as to develop an indication of borehole depth by means of conventional indicating equipment not depicted, The measuring wheel 15A may be suspended in any convenient manner, such as by a traveling block suspended over the borehole by a derrick.

The tubing locator 11 is necessarily of a type capable of seeing adjacent tubing strings in the borehole, as depicted in FIGURES 1 and 2, and is preferably composed of a shield 11A of radiation-opaque material, such as lead, tungsten, or uranium 23 8, and having two longitudinally arranged ports 11B and 11C arranged in one side thereof. A gamma ray source 20, preferably formed of an encapsulated quantity of iridium, is disposed in one port 11B, and a radiation detector 22 is disposed in the other port 11C. The detector 22 is preferably composed of two or more short Geiger-Muller tubes 22A arranged longitudinally within the port 11C. Suitable provision (not shown in FIGURE 3) is made to energize the detector 22, and to conduct the electrical output signals therefrom to the electronics section 13B and to the cable head 12. The shield 11A serves to collimate the radiation emitted by the source 20 into a laterally directed beam. As is more fully explained in the co-opending application Se-r. No. 64,016, now patent No. 3,175,608 which Was filed Oct. 21, 1960, by Billy F. Wilson, the gamma rays penetrate and become scattered and absorbed in the substances adjacent the tubing string 6 containing the subsurface perforating tool assembly 9. However, a portion of such scattered gamma rays become redirected into the tubing string 6, and pass into the port 11C where they may be sensed by the detector 22. Since the shield 11A restricts detection to only those gamma rays approaching the detector 22 along a relatively narrow path, it is apparent that the detector 22 will tend to see only gamma rays scattered within a very restricted angular portion or segment of the adjacent substances. Furthermore, since the scattering effect had on the gamma rays is directly related to the character of the scattering substances, the output of the detector 22 will be directly affected whenever the beam of gamma rays is aimed at an adjacent tubing string 5 or 7. Thus, the tubing locator 11 (and perforator may be rotated so as to scan the adjacent substances With the beam of gamma rays, and variations in the number of detected gamma rays provide an indication of the location of the adjacent tubing strings 5 and 7 with respect to the tubing string 6 containing the subsurface tool assembly.

Since it is an object of the present invention to perforate one tubing string without hitting any of the adjacent tubing strings, the charges 10A of the monodirectional tubing perforator 10 must be arranged in a known angular relationship to the lateral location of ports 11B and 11C of the tubing locator 11. As depicted in FIGURE 3, it is particularly useful that these charges 10A be positioned 180 degrees from the direction of the ports 11B and 11C, since the charges 10A may thus be fired at the position wherein the tubing locator 11 sees an adjacent tubing string 5 or 7, and thus the necessity for further rotation is thereby eliminated. However, any angular relationship may be used, provided such relationship is known.

Referring now to the rotator section 14, there may be seen an electric motor 16 fixedly mounted within a pressure-resistant housing 17. The shaft 18 is connected to monodirectionally drive a reduction gear assembly 19, which is arranged so that its output drive shaft 19A is aligned with the axis of the subsurface tool assembly, and which is fixedly attached to the tubing locator 11 in some suitable manner. FIGURE 3 shows the output drive shaft 19A extending through a packing gland 19B at the lower end .of the rotator section 14. However, any suitable means may be employed to prevent fluids in the borehole from entering the interior of the housing 17.

Any AC-driven motor may be utilized for the purpose of the electric motor 16, depicted in FIGURE 3, provided it will develop torque sufiicient to rotate the tubing locator 11 and tubing perforator 10. However, it is desirable that rotation be accomplished at a very slow rate in order that statistical errors in counting the detected gamma rays sensed by the detector 22 will be overcome as the tubing locator 11 is revolved. A desirable rotation speed has been found to be one full revolution in approximately eight minutes, and thus the reduction gear assembly 19 is employed to provide a suitable rotation speed.

As hereinbefore stated, it is desirable that the rotator section 14 provide an indication when a full revolution of the tubing locator 11 and tubing perforator 10 has been achieved. Thus, a cam 30 is mounted on the output shaft 19A to actuate a switch 32 upon completion of each such revolution. The switch 32, as may be seen in FIGURE 4, is adapted to be normally closed. Thus, the actuator 33 rides on the cam 30 to maintain the switch 32 in an open position, except when the actuator 33 encounters a notch 30A, whereupon the switch 32 is closed for 1015 seconds. As may be seen in FIGURE 4, the AC electric motor 16 is energized by means of AC power sent to the motor windings 34 via a single central conductor 36 in the cable 15. The AC electric motor 16 is preferably synchronous in character in order that it will operate at a constant speed irrespective of normal fluctuations in voltage or amperage which may be expected to occur, from time, to time, in the AC power sent downhole over the conductor 36. When the switch 32 is closed, however, a load resistor 35 is connected into the motor circuit which serves to substantially increase the amperage supplied during the 10-15 second interval within which the actuator 33 rides in and out of the notch 30A in the cam 30, and this momentary amperage increase may be observed at the surface as an indication of the completion of a revolution.

It may be seen that it is necessary to energize the AC electric motor 16 by means of a source of power located at the surface of the earth, and that it is necessary to conduct such power over the cable 15. Furthermore, it is necessary to actuate both the detector 22 and the tubing perforator 10, by means of power and control circuits located at the surface, and to conduct the detector 22 output signal to the surface. However, as is well known in the industry, it is not desirable to employ a multiconductor cable 15 for the present purposes, since multiconductor cables are much more expensive and are relatively short-lived. Moreover, the well pressures which are encountered make it extremely 'difiicult to insert the larger diameter, multi-conduc-tor cables into the boreholes. Accordingly, the cable 15 depicted in FIGURE 3 is preferably that which utilizes a single conductor 36 with a grounded armored sheath (not depicted) for a return circuit, and provision is made by the present invention for energizing and actuating the various circuits in the subsurface tool assembly 9 via the cable 15.

Referring now to FIGURE 5, there is depicted various power and recording equipment located at the surface, which equipment includes a master power supply 50, a power control circuit 52, shooting circuitry 54 for firing the tubing perforator 10, and a casing collar locator recorder 56 of conventional linear chart design for recording indications of the presence of tubing collars 4 in conjunction with the depth indications provided by the operation of the measuring wheel 15A. A polar-type of recorder 60 is also located at the surface for recording the output signal provided by the detector 22.

All of the depicted surface equipment may be of conventional design, and therefore need not be described herein in detail. The master power supply 50 is preferably any suitable source of 110 volt AC power, and the shooting circuitry 54 may be any suitable means actuated by the master power supply 50 and adapted to develop power of sufficient amperage and voltage to actuate the charges 10A in the tubing perforator 10. Accordingly, the shooting circuitry 54 preferably includes components of conventional design and arrangement for stepping up the voltage of the 110 volt AC power and suitable safety circuits for preventing accidental or spontaneous discharge of the charges 10A. In addition, provision should be included for rectifying the output of the shooting circuitry 54, so that a DC output will be derived which is of a preselected polarity different from the polarity of the other signals to be transmitted over the conductor 36. The power used to actuate the firing circuitry in the tubing perforator 10 is usually negative in polarity, whereas the balance of the tool 9 circuitry is usually adapted to be actuated by power of positive polarity. Accordingly, electrical signals and power may be transmitted to and from the surface equipment, and the detector 22, casing collar locator 13, rotator section 14, and other components in the electronics section 13B, without interfering with or inadvertently actuating the tubing perforator 10.

The power control circuit 52 is composed of conventionally designed and arranged circuits and components for receiving power outputs from the master power supply '50, and from the shooting circuitry 54, and for suitably processing and applying such outputs to the conductor 36 for transmission to the subsurface tool assembly 9. Accordingly, provision is preferably included for regulating the amount of AC power applied to the conductor 36 to actuate the electric motor 19, and to further adjust the voltage with respect to the length of cable 15 which has been paid into the borehole 2. Provision is also included for converting 110 volt AC energy to positive DC energy to develop power for energizing the circuits in the subsurface tool assembly 9 which serve the detector 22 and the casing collar locator 13. In addition, provision is included for supplying DC power to the filter-amplifier-discriminator circuitry 58, and also power to drive the chart drive mechanisms of the casing collar locator recorder 56 and the polar recorder 60. As hereinbefore stated, the chart drive of the casing collar locator recorder 56 is actuated in conjunction with the operation of the measuring wheel 15A, and therefore its action is relatively independent of the operation of the other components described herein. However, it is essential to the objects of the present invention that the chart drive of the polar recorder 60' be coordinated with the rotation of the tubing locator 11 and tubing perforator 10. Consequently, provision is also made to synchronize the application of AC power, by the master control circuit 52, to the chart drive of the polar recorder 60 with the application of AC power to the conductor 36 for driving the electric motor 19, so that the polar recorder 60 and electric motor 19 operate in, and only in, conjunction with each other.

As hereinbefore explained, the master control circuitry 52 includes provision for applying AC power to the electric motor 19 at a regulated preselected voltage, notwithstanding variations in the length of the cable 15, and at a regulated amperage to stabilize the speed of the electric motor 19. Any suitable means, such as an ammeter of conventional design, may be incorporated in the master control circuitry 52 for monitoring the amperage of the AC current used to drive the electric motor 19. Accordingly, when the actuator 33 of the switch 32 rides into the notch 30A in the cam 30, as is depicted in FIGURES 3 and 4, the additional amperage drawn by the load resistor 35 will be readily apparent and may easily be observed as an indication each time the tubing locator 11 and .tubing perforator 10 have completed a revolution.

Referring again to FIGURE 5, there may be seen other circuits of conventional design which compose the electronics section 13 of the subsurface tool assembly 9, in-

eluding decoupler and filter circuits 62, a rectifier 64, a DC-DC converter 66, and discriminator and amplifier circuits 6 8. It is the purpose of the decoupler and filter circuits 62 to decouple the DC and AC currents transmitted via the conductor 36, and to filter out all AC from the DC current passing to the detector 22 and the casing collar locator 13 circuits. Low voltage DC current from the decoupler and filter circuits 62 is applied to energize the discriminator and amplifier circuits 68, which receive and process signals produced by the detector 22 and the casing collar locator 13. The low voltage DC is also connected to the DC-DC converter 66 which converts it into regulated high voltage DC for use in energizing the Geiger-Muller tubes 22A in the detector 22.

As hereinbefore stated, it is the purpose of the shooting circuitry 54 to develop a high voltage DC voltage, of a negative polarity, to energize the firing circuitry in the tubing perforator 10. This negative high voltage DC cur-rent is passed through rectifier 64 to eliminate any AC components, before being applied to the tubing perforator 10. It is preferable that the firing circuitry in the tubing perforator 10 be adapted to respond only to a relatively high amperage current, in order to avoid being inadvertently actuated by other currents on conductor 36. Accordingly, the output of the rectifier 64 is preferably a DC current of 250-300 milliamps, whereas the high voltage DC signals utilized by the detector 22 and easing collar locator 13 circuitry are preferably limited to currents of about 30-40 milliamps. These particular amperages are not considered critical, however, but are merely examplary.

Of course, an important factor afiecting the optimum use of the present invention is the proximity of the wall of the borehole 2- to the subsurface tool assembly 9. In many cases the materials composing the earth formations traversed by the borehole 2 are constituted of substances such as limestone or dolomite, and these substances have a density approximately the same as that of a hollow steel tubing joint 3. Since it is necessary to perforate the wall of the borehole 2, as well as the tubing string 6, it is desirable to locate the nearest section of the wall of the borehole 2 while locating the adjacent tubing strings 5 and 7. Moreover, if the wall is located at the same time the adjacent tubing strings 5 and 7 are located, this will serve as verification of the readings displayed by the polar recorder 60, and serve to reduce the possibility of a misinterpretation.

Referring now to FIGURE 6, there is depicted a polar plot intended to represent the view of the borehole 2 shown in FIGURE 2. As hereinbefore explained in connection with FIGURES 3 and 5, the detector 22 develops an output signal which is indicative of the gamma rays which are scattered in the substances surrounding the tubing locator 11 and which reenter the tubing string 6 along a relatively narrow path leading into the port 11C containing the detector 22. The detector 22 has been stated to be composed preferably of a plurality of short Geiger-Muller t-ubes 22A, although other types of radiation-sen sing equipment such as a scintillation counter may be found acceptable. Irrespective of the type of detector 22 used for present purposes, however, the output signal will be composed of a series of positive DC pulses functionally related to the incident gamma rays, and thus this signal must be passed to a count rate meter 59 which provides an output signal voltage indicative of the rate of such incidence. This voltage is then applied to the polar recorder 60 which displaces a pen and ink recording of such voltage output from the count rate meter 59 in the form of magnitudes of pen deflection from a central index or zero. That is, the greater the voltage or count rate, the greater will be the deflection of the pen from zero, and since the chart drive mechanism of the polar recorder 60 is adapted to revolve the chart about its zero, as the tubing locator 11 and tubing perforator 10 are revolved by the rotator section 14, a generally circular trace will be developed during a single rotation which is indicative of the character of the contents of the borehole 2 with respect to the tubing string 6.

Accordingly, FIGURE 6 shows a typical chart 60 displaying a trace 62 developed during one complete rotation, and showing how the deflection of the pen from zero 64 has varied during such rotation. The relatively sharp decreases in gamma ray incidence upon the detector 22, when the beam of gamma rays passes the adjacent tubing strings 5 and 7, are shown by vectors 72 and 73 which correspond to arrows B and A in FIGURE 2. The gradual but substantial decrease in counting rate is indicated by vector 74 which corresponds to arrow C, in FIGURE 2, indicating the nearest portion of the wall of the borehole 2. Of course, FIGURES 2 and 6 are drawn to indicate an ideal situation, where the tubing strings 5-7 are equilaterally spaced within the borehole 2 and from each other, and where the borehole 2 is absolutely circular with no unilateral cavings or washouts opposite the tubing locator 11. In many cases, the tubing strings S-7 are badly entwined or otherwise irregularly arranged within the borehole 2, and the readings provided on the chart 60 will require skilled interpretation. Nevertheless, apparatus and methods described and depicted herein have been employed to accurately find adjacent tubing strings in such boreholes, and have permitted selective perforation of such strings without striking the adjacent strings.

The apparatus and methods depicted and described herein are intended to be exemplary, and numerous variations and modifications may obviously be made without departing from the concept of the present invention. Accordingly, it should be clearly understood that the forms of the invention disclosed herein are intended to be illustrative only, and are not intended to limit the scope of the invention.

What is claimed is:

1. Apparatus for selectively perforating a selected tubing string in a borehole, said apparatus comprising a mondirectional perforator for insertion in said selected tubing string and including a tubing locator for detecting the positions of an adjacent tubing string and the nearest portion of the wall of the borehole relative to said selected tubing string,

rotator means for rotating said locator and perforator and including an electric motor and signalling means for indicating the completion of a full revolution of said locator and perforator,

an armored and grounded cable having a single conductor and attached at one end to said rotator, locator and perforator, and

power and indicating means connected to the other end of said cable and including recording means functionally interconnected with said locator and said rtator for developing a polar-type representation of said positions of said adjacent tubing string and nearest portion of borehole Wall.

2. Apparatus for selectively perforating a selected tubing string in a borehole, said apparatus comprising tubing detector and perforator means for insertion in said selected tubing string and including means for deriving a first electrical indication functionally related to the positions of an adjacent tubing string and the nearest portion of the wall of the borehole relative to said selected tubing string,

rotator means including an AC-actuated electric motor interconnected with said detector and perforator means,

said rotator means further including means for deriving a second electric indication related to the completion of each full revolution of said detector and perforator means,

a source of AC power including indicating means responsive to said second electrical indication, recording means interconnected with said source of AC power for deriving in response to said first electrical indication a polar graph representative of said positions of said adjacent tubing string and nearest portion of said borehole wall, and a grounded armored cable having a single conductor interconnected at one end to said source and said recording means and at the other end to said rotator means and said detector and perforator means.

3. Apparatus for selectively perforating a tubing string,

said apparatus comprising a monodirectional tubing perforator,

a tubing locator fixed to said perforator and having means to derive an electrical signal functionally related to the character of the substances adjacent said one tubing string,

'an electrically-driven rotator for rotating said tubing locator and having means for developing an indication of the rotation of said tubing locator and said tubing perforator,

a grounded armored cable having a single electrical conductor arranged to conduct signals between the surface of the earth and said tubing perforator, tubing locator, and rotator, and

a polar recorder operating synchronously with said rotator and interconnected with said conductor to receive andrecord said electrical signal derived by said tubing locator.

4. Apparatus for selectively perforating a selected tubing string in a borehole, said apparatus comprising tubing detector and perforator means for insertion in said selected tubing string and including means for deriving a first electrical indication functionally related to the positions of an adjacent tubing string and the nearest portion of the wall of the borehole relative to said selected tubing string, rotator means including an AC-actuated electric motor interconnected with said detector and perforator means, said rotator means further including means for deriving a second electrical indication related to the completion of each full revolution of said detector and perforator means, a source of AC power including indicating means responsive to said electrical indication, recording means interconnected with said source of AC power for deriving in response to said first electrical indication a polar graph representation of said positions of said adjacent tubing string and nearest portion of said borehole Wall, a grounded armored cable having a single conductor interconnected at one end to said source and said recording means and at the other end to said rotator means and said detector and perforator means, means interconnected with said rotator means and said tubing detector and perforator means to derive a third electrical indication relative to collars in said selected tubing string, and linear recording means interconnected with said source of AC power for deriving in response to said third electrical indication a graphic representation of the location of said collars in said borehole relative to depth. 5. Apparatus for selectively perforating a selected tubing string in a borehole, said apparatus comprising tubing detector and perforator means for insertion in 6 said selected tubing string and including means for deriving a first electrical indication functionally related to the positions of an adjacent tubing string and the nearest portion of the wall of the borehole relative to said selected tubing string,

rotator means including an AC-actuated electric motor interconnected with said detector and perforator means,

said rotator means further including means for deriving a second electrical indication related to the com- 11 pletion of each full revolution of said detector and perforator means,

a source of AC power including indicating means responsive to said electrical indication,

recording means interconnected with said source of AC power for deriving in response to said first electrical indication a polar graph representation of said positions of said adjacent tubing string and nearest portion of said borehole Wall,

a grounded armored cable having a single conductor interconnected at one end to said source and said recording means and at the other end to said r0- tator means and said detector and perforator means,

means interconnected with said rotator means and said tubing detector and perforator means to derive a third electrical indication relative to collars in said selected tubing string,

linear recording means interconnected with said source of AC power for deriving in response to said third electrical indication a graphic representation of the location of said collars in said borehole relative to depth,

vcontrol means interconnected with said source of AC power, and actuating means in said perforator means for actuating said perforator in response to said control means.

References Cited UNITED STATES PATENTS 7/1958 Tanguy 16655 X 8/ 1960 Iosendal et al.

11/1960 Pfefferle l75-40 X 8/1961 True 16655 1/1963 Morse et al 16635 X 7/1963 Terrel 16635 9/1963 Kenneday et al. 16655.1 8/1964 Nelson 16635 8/ 1964 Pennebaker 1664 10/1964 Lanmon 16655.1 3/1965 Wilson 166-4 FOREIGN PATENTS 12/ 1960 France.

6/1961 France.

OTHER REFERENCES Lebourg, M. P. and Bell, W. T. Perforating of Mul- CHARLES E. OCONNELL, Primary Examiner. 25 DAVID n. BROWN, Examiner. 

1. APPARATUS FOR SELECTIVELY PERFORATING A SELECTED TUBING STRING IN A BOREHOLE, SAID APPARATUS COMPRISING A MONODIRECTIONAL PERFORATOR FOR INSERTION IN SAID SELECTED TUBING STRING AND INCLUDING A TUBING LOCATOR FOR DETECTING THE POSITIONS OF AN ADJACENT TUBING STRING AND THE NEAREST PORTION OF THE WALL OF THE BOREHOLE RELATIVE TO SAID SELECTED TUBING STRING, ROTATOR MEANS FOR ROTATING SAID LOCATOR AND PERFORATOR AND INCLUDING AN ELECTRIC MOTOR AND SIGNALLING MEANS FOR INDICATING THE COMPLETION OF A FULL REVOLUTION OF SAID LOCATOR AND PERFORATOR, AN ARMORED AND GROUNDED CABLE HAVING A SINGLE CONDUCTOR AND ATTACHED AT ONE END TO SAID ROTATOR, LOCATOR AND PERFORATOR, AND POWER AND INDICATING MEANS CONNECTED TO THE OTHER END OF SAID CABLE AND INCLUDING RECORDING MEANS FUNCTIONALLY INTERCONNECTED WITH SAID LOCATOR AND SAID ROTATOR FOR DEVELOPING A POLAR-TYPE REPRESENTATION OF SAID POSITIONS OF SAID ADJACENT TUBING STRING AND NEAREST PORTION OF BOREHOLE WALL. 